The present invention relates to a thermal imaging apparatus, by which a plurality of thermal images of an observed object corresponding to different times are simultaneously displayed on respective parts of a television monitor screen, to allow obtaining more information concerning the object from the combination of the thermal images, by comparing them with each other.
A thermal imaging apparatus provides a thermal image by receiving passively the infrared radiation from an observed object with an infrared sensor or detector. The technology concerning the thermal imaging apparatus has become known as "thermography", and is useful in the medical and industrial fields for non-invasive diagnosis and non-destructive examination.
The thermal imaging apparatus generally provides a thermal image by means of an optical scan and an electronic display which are synchronized with each other. However, the optical scanning speed cannot be increased as high as the television (TV) scanning speed because of the well known thermography principle. Therefore, a conversion technique which converts the speed of the optical scan to that of the TV display is required to observe and record thermal images using a conventional TV monitor and a video tape recorder.
The conversion can be provided using a memory device, such as a hard memory formed of a semiconductor integrated circuit (IC memory). In this case, the signal data detected by the optical scan at relatively slow speed are memorized in the IC memory, and the memorized data are read out and displayed by the TV technique.
In thermography it is often required to check the time variation of the thermal image of an observed object, because the variation provides valuable information. The thermal images at different times will be referred to as the "thermal time images" hereinafter.
In the method of display in the prior art, the variations of the thermal time images could be compared by observing different thermal time images sequentially displayed on the TV monitor. Therefore, when comparison between the thermal time images was required, hard copies of the thermal time images had to be provided, such as photographs.
In a typical imaging apparatus, a method has been employed for simultaneously displaying different images on an electronic displaying device, such as a TV monitor, using a large memory device such as a large IC memory which has a large memory capacity. The method is as follows: the data of each different image is memorized in a respective part of the large IC memory, sequentially, and all the memorized data are read out by the TV technique and simultaneously displayed on respective parts of a TV monitor. With this method, however, a lot of memory elements (dot memories) and a complicated write-in and read-out control means are required. Therefore, is is difficult to economically apply this method to an actual thermal imaging apparatus. Consequently, this has been a major problem for economically realizing simultaneous display of thermal time images on a TV monitor in a thermal imaging apparatus.